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REFINERY TECHNOLOGY
www.oilgaspublisher.de112 45. Edition · Issue 4/ 2019
Feed properties effect on the performance of
vacuum residue ebullated bed H-Oil
hydrocracking
(Photo: stock.adobe.com)
By D. STRATIEV, I. SHISHKOVA, E. NIKOLAYCHUK, W. IJLSTRA, B. HOLMES and M. CAILLOT*
*
Dr. Dicho Stratiev, Dr. Ivelina Shishkova, Ekaterina
Nikolaychuk , LUKOIL Neftohim Burgas AD, Wessel
Ijlstra, Shell Catalysts and Technologies; Blaine Hol-
mes, Shell Catalysts and Technologies; Dr. Maxime
Caillot, Axens.
E-mail: stratiev.dicho@neftochim.bg
0179-3187/19/12 DOI 10.19225/1912xx
© 2019 EID Energie Informationsdienst GmbH
Abstract
24 vacuum residual oils originating from 15
crudes and three imported atmospheric residu-
al oils were processed in the LUKOIL Neftohim
Burgas (LNB) ebullated bed vacuum residue
(EBVR) H-Oil hydrocracking unit. During
their processing the sediments content in the at-
mospheric tower bottom (ATB) product, that
correlates with the rate of fouling of the H-Oil
equipment, was kept at approximately 0.4%.
At this level of sediments in the ATB product
the conversion was found to increase with the
feed colloidal instability index (CII) reduction
and asphaltene conversion enhancement. It
was found that asphaltenes from the feed
100% Urals VR participate more readily in re-
combination reactions in comparison with the
asphaltenes coming from crudes from Middle
East. This leads to a decrease in the value of
asphaltene conversion and to an increase of se-
dimentation. The reduction of feed CII and im-
provement of asphaltene conversion allows an
increase in the hydrocracking reaction severity,
resulting in a higher VR conversion and high-
er yields of higher value products at the expen-
se of the lower yield of the lower value VTB
product.
1 Introduction
Performance of heavy oil conversion pro-
cesses is the driving force for profitability
of modern petroleum refining. The rea-
son for this is the ability of the heavy oil
conversion processes to convert the lower
value heavy, black crude fractions into
high value light oil products (automotive
fuels and feeds for petrochemical pro-
ducts-propylene, butylenes, naphtha,
etc.). The fluid catalytic cracking (FCC) of
vacuum gas oil was the best profit perfor-
mer in the LUKOIL Neftohim Burgas
(LNB) refinery when its heavy oil conver-
sion process scheme consisted of FCC of
vacuum gas oil and visbreaking of vacu-
um residue. However, subsequent to the
commissioning of the ebullated bed vacu-
um residue (EBVR) H-Oil hydrocracking
(in July 2015) H-Oil has become the best
profit performer in the LNB refinery, out-
weighing the FCC in its significance for
profit improvement. Among all process
variables the feedstock quality was found
to be the single variable that has the big-
gest impact on heavy oil conversion pro-
Don't hesitate to contact us and share your opinion,
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REFINERY TECHNOLOGY
www.oilgaspublisher.de 11345. Edition · Issue 4/ 2019
cesses [1, 2]. This was also confirmed for
the H-Oil process, where the difference
between conversions observed during hy-
drocracking of vacuum residual oils with
different properties amounted to 20%
(between 55 and 75% conversion) [3].
The main limitation that restricts conver-
sion level enhancement in EBVR hydro-
cracking is sedimentation [4]. The sedi-
ments level in the H-Oil residual oils con-
trols equipment fouling and governs the
H-Oil unit cycle duration between two
consecutive cleanings. Any unplanned
shut-down for cleaning the H-Oil unit
has a strong negative affect on the econo-
mics of petroleum refining. A one day
down-time of the H-Oil hydrocracker is
equivalent to about 0.6 million US-$ loss
of profit opportunity. It was found that in
the LNB EBVR H-Oil hydrocracker the
dependence of sediment content in the
ATB product on conversion level is stron-
gly affected by the origin of the processed
vacuum residual oils. In order to under-
stand which properties of the vacuum re-
sidual oils originating from 15 crudes and
three imported atmospheric residual oils
processed in the LNB refinery affect H-Oil
performance, the feedstock vacuum resi-
dual oils were characterized and the per-
formance of the H-Oil hydrocracker was
related to the properties of the studied
feedstocks. The aim of this work is to find
out which feedstock properties control
the conversion level in the EBVR H-Oil
hydrocracker at approximately the same
content of sediments in the H-Oil ATB
product.
2 Experimental
2.1. Materials
24 vacuum residual oil feedstocks of the
LNB EBVR H-Oil hydrocracker, obtained
from blending 15 crudes and three im-
ported atmospheric residual oils in diffe-
rent ratios, were characterized in this stu-
dy. Their physical and chemical properties
are summarized in Table 1. The catalyst
employed in this study was a commercial
Ni-Mo low sediment catalyst.
2.2. Procedures
All hydrocracking experiments were car-
ried out in the LNB EBVR H-Oil hydro-
cracker. A simplified process diagram of
the LNB EBR H-Oil hydrocracker is pre-
sented in [4]. Details about the LUKOIL
Neftohim Burgas H-Oil residue hydrocra-
cker are given in [5]. The operating con-
ditions in the LNB EBR H-Oil hydrocra-
cker whilst processing the 24 vacuum re-
sidual oil feedstocks are summarized in
Table 2.
The vacuum residue 540°C+ conversion
was estimated by the equation:
540 540
540
Pr
(%) 100
CC
C
EBRHCFeed EBRHC oduct
Conversion EBRHCFeed
(1)
where, EBRHCFeed540°C+=weight of the
EBRHC feed fraction boiling above 540°C,
determined by high temperature simula-
ted distillation, method ASTM D 7169;
EBRHCProduct540°C+=weight of the
EBRHC product fraction boiling above
540°C, determined by high temperature
simulated distillation, method ASTM D
7169.
The C5-, and C7-asphaltene conversions
were calculated by the equation:
Pr
_ (%) *100
FeedAsp oductAsp
Asphaltene conversion FeedAsp
(2)
where,FeedAsp=Asphaltene (C5, or C7-
asphaltenes) content in the feed, %;
ProductAsp=Asphaltene (C5, or C7-as-
phaltenes) content in the products, %;
A second order kinetic conversion, a
measure of the severity employed in the
LNB EBVR H-Oil hydrocracker, was esti-
mated by the equation:
00
exp exp
/(1 )
aa
EE
kk
RT RT
XLHSV LHSV
(3)
where, X=second order kinetic conversi-
on,%
k0=pre-exponential factor in Arenius’
equation; k0= 1.89x1012, l.mole-1.s-1
Tab. 1 Physical and chemical properties of the H-Oil vacuum residual oil feeds under study
Nr. Feed D15, g/
cm3
Feed
CCR,
wt.%
Feed VIS
(70%
VR/30%
HCO) at
80°C,
mm2/s
Softe-
ning
point, °C
S, wt.% Satura-
tes, wt.%
Aroma-
tics,
wt.%
Resins,
wt.%
C7-asph,
wt.%
C5-asph.,
wt.%
C7-asph.
D15, g/
cm3
C5-asph.
D15, g/
cm3
Feed CII
(C5-asp)
Feed CII
(C7-asp)
1 1.010 18.2 182.2 34.8 3.91 21.9 55.8 14.4 7.8 19.0 1.175 1.166 0.69 0.42
2 1.007 17.2 170.6 33.5 3.63 23.0 54.7 13.5 8.9 19.2 1.169 1.162 0.73 0.47
3 1.005 19.3 190.9 33.7 3.55 23.7 56.0 10.3 10.1 16.2 1.140 1.162 0.66 0.51
4 1.012 19.8 176.5 3.17 21.1 55.3 13.2 10.4 21.1 1.159 1.179 0.73 0.46
5 1.007 15.6 162.7 3.24 22.9 54.4 13.9 8.8 19.7 1.198 1.136 0.74 0.46
6 1.007 15.9 145.4 3.08 23.0 54.6 10.3 12.1 19.3 1.158 1.140 0.73 0.54
7 0.996 14.0 103.3 26.2 3.27 27.6 48.1 16.6 7.8 22.1 1.207 1.132 0.99 0.55
8 1.012 16.8 162.7 0.0 3.59 21.3 53.0 15.5 10.2 24.2 1.200 1.118 0.83 0.46
9 1.016 17.2 176.6 36.1 3.92 20.0 56.5 13.7 9.8 20.9 1.180 1.139 0.69 0.42
10 1.016 17.5 172.9 3.61 20.0 54.4 15.8 9.8 24.0 1.212 1.124 0.79 0.43
11 1.000 15.6 144.8 34.3 3.51 25.7 48.8 7.8 17.8 23.9 1.140 1.144 0.99 0.77
12 1.008 17.7 150.3 3.46 22.8 52.1 14.4 10.7 23.3 1.127 1.135 0.86 0.50
13 0.996 15.9 160.0 36.0 2.91 27.6 48.0 11.7 12.7 22.2 1.183 1.118 0.99 0.67
14 1.013 18.1 148.5 3.66 20.8 55.4 8.5 15.4 21.4 1.156 1.153 0.73 0.57
15 1.006 18.1 158.1 3.61 23.2 51.9 9.2 15.7 22.9 1.190 1.137 0.86 0.64
16 1.001 16.3 132.9 3.24 25.2 50.5 14.3 10.0 22.1 1.222 1.139 0.90 0.54
17 1.008 16.9 144.5 3.55 22.8 53.8 10.1 13.3 20.8 1.190 1.169 0.77 0.57
18 1.008 16.2 125.2 27 3.69 22.8 53.9 10.8 12.5 20.5 0.76 0.55
19 1.014 14.8 117.5 3.33 20.5 57.7 12.1 9.7 18.4 0.64 0.43
20 1.022 16.6 94.4 24.0 3.13 18.2 59.3 12.6 9.9 19.4 0.60 0.39
21 1.008 15.2 3.04 22.6 57.3 9.2 10.9 15.9 0.62 0.50
22 1.025 15.9 3.44 17.5 59.8 8.2 14.5 19.7 0.59 0.47
23 1.021 3.64 18.5 58.7 9.8 13.0 19.8 0.62 0.46
24 1.021 16.7 3.22 18.6 61.1 7.5 12.8 16.1 0.53 0.46
REFINERY TECHNOLOGY
www.oilgaspublisher.de114 45. Edition · Issue 4/ 2019
Ea = activation energy in Arenius’ equati-
on; Ea= 190.9 kJ/mole
R=universal gas constant=8.314 kJ/mol°K
T=reaction temperature, °K
The values of activation energy (Ea) and
pre-exponential factor (k0) in Arenius’
equation were determined in a previous
study [6].
2.3 Analyses
The H-Oil vacuum residual oil feedstocks
were characterized for their SARA (satu-
rates, aromatics, resins, asphaltenes) com-
position in accordance with the procedure
described in [7]. The densities of the C5-
and C7-asphaltenes were measured indi-
rectly from the densities of a series of so-
lutions of asphaltenes and maltenes in to-
luene at different concentrations as de-
scribed in [8]. Solutions of asphaltene in
toluene at concentrations up to an asphal-
tene mass fraction of 3% were prepared.
Solutions of maltenes in toluene at con-
centrations up to a maltene mass fraction
of 6% were prepared. The same procedu-
re was applied for measurement of the
densities of the vacuum residual oils un-
der study. This course of action was selec-
ted to avoid possible errors in measure-
ment of the densities of the investigated
vacuum residual oils. It was documented
in our previous work that errors could be
encountered in the measurement of vacu-
um residual oil density if no dilution with
high aromatic solvent was applied [9].
The repeatability of C5-asphaltenes was
determined to be ±0.023 g/cm3, while
that of C7-asphaltenes was ±0.036g/cm3.
The Conradson carbon content of the stu-
died vacuum residual oils was measured
according to the ASTM D189- 06(2014)
method. The kinematic viscosity of blends
of the vacuum residual oils under study
with FCC HCO (70% VRO / 30% FCC
HCO) were measured in accordance with
ASTM D445-18 method. Properties of the
diluent FCC HCO used in this study are
given in [4]. The softening point of the
vacuum residual oils under study was
measured according to ASTM D6493-
11(2015) method.
3. Results and discussion
The sediment content in all studied H-Oil
residual oils in this work resulted from as-
phaltene agglomeration, since the ash
content, a measure of inorganic sedi-
ments, was zero, and since the content of
toluene insoluble, a measure of the pre-
sence of coke particles, was also zero. In
order to evaluate which parameters have
an influence on conversion, a correlation
matrix of the data from Tables 1 and 2 was
prepared. Table 3 presents a summary of
the correlation matrix that shows only the
variables, that have a statistically me-
aningful correlation (R≥0.75) with vacu-
um residue (VR) conversion. The data in
Table 3 indicates that conversion, under-
standably, correlates well with the opera-
ting conditions and reaction temperature,
reaction delta T and the second order con-
version that reflects reaction severity (re-
action temperature and LHSV at fixed ac-
tivation energy and pre-exponential fac-
tor as seen from Equ. 3). From the feed-
stock properties the saturates content,
aromatics content, and CIIC5asp correlate
statistically meaningfully with the conver-
sion. The C5 asphaltene conversion is very
close to the statistically meaningful corre-
lation with the feed conversion (R=0.73),
while the C7 asphaltene conversion has a
y = 1x + 3E-12
R² = 0,9105
50
55
60
65
70
75
80
85
50 55 60 65 70 75 80 85
Measured Conversion,%
Estimated Conversion,%
Fig. 1 Agreement between estimated by Equ. 4 vacuum residue conversion and the measured one
y = 0,0043x + 0,912
R² = 0,6203
y = 0,0041x + 0,9704
R² = 0,3827
1,000
1,040
1,080
1,120
1,160
1,200
1,240
1,280
1,320
1,360
55 60 65 70 75 80 85
VTB C5- and C7- asphaltenes D15 g/cm3
VR conversion,%
VTB C5-asph. D15, g/cm3 VTB C7-asph. D15, g/cm3 VTB C7-asph. D15, g/cm3 from 100% Urals VR conversion of 64.7%
Fig. 2 Dependence C5- and C7-asphaltene density on VR conversion
50 55 60 65 70 75 80
Product yields,%
VR conversion,%
Naphtha Diesel VGO VTB
Fig. 3 Dependence of the H-Oil product yields on VR conversion
REFINERY TECHNOLOGY
www.oilgaspublisher.de 11545. Edition · Issue 4/ 2019
very low correlation coefficient with the
VR conversion (R=43). The lack of corre-
lation of the asphaltene conversion to the
VR conversion could mean a different re-
activity of the asphaltenes in comparison
with that of the other VR compounds: re-
sins, aromatics and saturates, or a pre-
sence of reactions through recombination
of asphaltenes. A higher rate of the reac-
tions of asphaltene recombination would
mean a higher content of asphaltenes in
the H-Oil products, which in turn would
lead to a lower value of the asphaltene
conversion as estimated by Equ. 2. Zhang
et al [10] have shown that the asphaltene
conversion follows second-order kinetics,
implying that the reaction of asphaltene
conversion might undergo a complicated
mechanism. Ramírez et al [11] have re-
ported second-order kinetics of the vacu-
um residue. Some researchers have repor-
ted first-order kinetics for both asphaltene
conversion [12, 13] and the whole vacu-
um residue [14]. Regardless of the order,
irrespective of the fact that the whole va-
cuum residue and its asphaltene fraction
are complex mixtures, consisting of myri-
ad components with different reactivities,
which seem to disappear asymptotically in
a second-order fashion [15], both the va-
cuum residue and the asphaltene conver-
sions should simultaneously increase with
reaction time, and reaction temperature.
However, the data for catalytic hydrocra-
cking of three different vacuum residual
oils reported in [16] have shown that as-
phaltene conversion does not increase
with the vacuum residue conversion in
the vacuum residue conversion range 55-
74%. This supports the thought that the
asphaltene conversion estimated by Equ.
2 reflects not only the real conversion of
asphaltenes to gas, liquid, and toluene in-
solubles (coke) [10], but also the recombi-
nation of asphaltenes. The recombination
of asphaltenes is the contributor to the
asphaltene conversion drop observed in
[16].
In order to examine the effect of VR con-
version on asphaltene conversion whilst
processing 100% Urals feed and blends of
Urals with imported atmospheric residue
and Middle East crudes, a comparison of
the SARA data of the feed and VTB, and
C5-asphaltene and C7-asphaltene conver-
sion was made. This comparison is pre-
sented in Table 4. This data shows that the
increase of conversion of 100% Urals VR
from 55.3 to 64.7% leads to a decrease of
C7-asphaltene conversion from 49.7 to
40%. The VTB C7-asphaltene density in-
creases from 1.157 at a VR conversion of
55.3% to 1.266 at a VR conversion of
64.7%. These facts suggest that the rate of
recombination of asphaltenes at a VR con-
version of 64.7% is higher than that at a
VR conversion of 55.3% and the C7-as-
phaltenes at VR conversion of 64.7% ha-
ve become less soluble due to their higher
density (higher aromaticity, which corre-
lates with density [17]). The data in Figu-
re 1 indicates that with the increase of VR
conversion the asphaltenes in the VTB
product become denser. It is also evident
from this data that the density of the VTB
C7-asphaltenes obtained from 100% Urals
VR at 64.7% conversion does not deviate
from the regression line made from the
data of the 24 studied VR feedstocks. In
other words the excessively high sedi-
ment content in the VTB (4%, correspon-
ding to 2.2% sediments in the ATB) obtai-
ned from 100% Urals VR at 64.7% cannot
be ascribed to the very high density and
therefore the very low solubility of the as-
phaltene fraction. The data in Table 4
shows that the same density of the VTB
C7-asphaltenes (1.265 g/cm3) with the
feed 85% Urals/15% BL (the last right
hand column of Table 4) and the much
higher C7-asphaltenes content (21.3%
versus 12.0% in the case 100% Urals at
64.7% VR conversion) has a 0.4% sedi-
ment content (versus 2.2% in the case
100% Urals at 64.7% VR conversion).
This suggests that the contribution to the
sediment content of the different residual
oil components is very difficult to assess
only on the basis of the VTB SARA analy-
ses and the VTB asphaltenes density. It is
evident from the data in Table 4 that the
content of aromatics in the VTB falls in all
studied hydrocracking cases, the resins
can go down or up, and the asphaltenes
increase during the hydrocracking. The
Tab. 2 H-Oil Operating conditions, vacuum residue and asphaltene conversions of the studied 24 feeds
Nr. Conversion, wt.% 2nd order con-
version,%
% of design ca-
pacity, %
React. temp.,
design tempera-
ture + or - t, °C
Reactor ΔT ATB HFT, wt.% C5 asp. Conv.,% C7 asp. Conv.,%
1 75 75.9 58.8 -4 124.2 0.23 72.4 67.5
2 69 69.9 76.7 -4 109.5 0.41 57.4 76.3
3 70.4 68.15 99.7 -1 102.4 0.38 52.6 55.0
4 74.9 73.5 76.7 0 115.4 0.36 67.8 64.9
5 64.6 68.5 76.7 -4 99.1 0.44 57.7 35.2
6 64.2 65.3 89.5 -4 91.6 0.38 53.8 54.7
7 58.5 63.8 89.5 -5 93.2 0.46 52.1 42.2
8 67.5 70.2 73.5 -4 106.3 0.42 65.1 47.6
9 73.0 76.3 75.4 0 125.3 0.16 63.1 60.0
10 67.3 71.3 74.8 -3 103.9 0.53 60.9 50.9
11 61.3 66.2 79.9 -7 94.4 0.42 53.2 60.4
12 62.0 65.9 75.7 -8 98.0 0.65 54.8 62.0
13 55.3 55.4 91.4 -13 89.5 0.32 50.8 44.5
14 72.3 73.3 79.9 +1 116.3 0.38 64.5 68.1
15 67.4 70.4 82.1 -2 106.4 0.42 63.9 66.0
16 65.8 68.2 86.9 -2 102.5 0.50 59.2 64.9
17 64.9 68.3 92.7 -1 101.2 0.49 58.7 59.3
18 72.5 74.5 78.0 +1 117.3 0.30 65.3 62.2
19 75.3 76.0 78.3 +3 122.9 0.10 61.8 52.9
20 81.2 77.9 78.6 +6 114.3 0.36 77.6 62.0
21 70.7 75.1 84.0 +3 111.0 0.39 52.0 42.8
22 74.3 77.8 85.0 +7 125.0 0.20 64.2 59.5
23 72.7 76.6 78.3 +4 120.0 0.370 66.7 54.9
24 75.7 78.0 79.6 +6 125.0 0.290 55.0 65.3
REFINERY TECHNOLOGY
www.oilgaspublisher.de116 45. Edition · Issue 4/ 2019
asphaltene density increases with the in-
crease of VR conversion, possibly due to
dealkylation of the side chains linked to
the aromatic rings. It is known that this
reduces their solubility [17, 18], however
the data in Table 4 indicate that VTB with
a denser and higher amount of asphalte-
nes has less sediment content than the
VTB in the case 100% Urals at 64.7% VR
conversion. If one compares the case
100% Urals at 64.7% VR conversion with
the case 64%Urals/15%BL/21%AR
(67.3% VR conversion) it can be seen that
both cases have the same values of the
2nd order conversion (64.4%), which
means the same reaction severity. The C7-
asphaltene conversion, however, in the
case 64% Urals/15% BL/21% AR is
55.3%, while in the case 100% Urals at
64.7% VR conversion is 40%. This sug-
gests that the 100% Urals VR asphaltenes
have a higher rate of recombination reac-
tions than the blended feedstock 64%
Urals/15% BL/21% AR. The case 100%
Urals at 64.7% VR conversion differs from
all studied cases shown in Table 4 with the
lowest asphaltene conversion (40%). The
reduction of Urals content of the LNB H-
Oil VR feedstock has the effect of increa-
sing the asphaltene conversion, which
suggests that the Urals asphaltenes are
more prone to recombination reactions
due to some other characteristics, which
have not been measured in this work. The
asphaltene density did not prove to be a
reliable indicator for their solubility and
propensity to form sediments. The asphal-
tene recombination reactions may form
oiligomerized new asphaltene species,
which might have a higher inclination to
form sediments. The asphaltene conversi-
on seems to be a good indicator for a
quantitative assessment of the asphaltene
recombination reactions.
By combination of the parameters H-Oil
feed CII (C5) and the C5 asphaltene con-
version the following equation predicting
VR conversion was obtained:
68.9 32.8 ( 5 ) 0.411 . . 0.954VRconversion FeedCII C asp asp conv R
(4)
where,
Feed CII (C5-asph)=H-Oil feed col-
loidal instability index based on C5-asphal-
tenes
C5-asp.conv.=C5-asphaltenes conversion, %
Figure 2 shows a good agreement bet-
ween measured and estimated by Equati-
on 4 conversions. Equation 4 indicates
Tab. 3 Correlation matrix of conversion and variables which statistically meaningfully correlate
Conv 2nd order
Conv.
TRX
Sat
ARO Feed CII (C5) Feed CII (C7)C
5 asp.
Conv.,%
C7 asp.
Conv.,%
Conv 1.00
2nd order Conv. 0.93 1.00
TRX 0.85 0.89 1.00
ΔT 0.88 0.92 0.77
Sat -0.83 -0.86 -0.79 1.00
ARO 0.87 0.86 0.85 -0.90 1.00
Feed CII (C5) -0.85 -0.83 -0.83 0.84 -0.99 1.00
C5 asp. Conv.,% 0.73 0.66 0.47 -0.63 0.45 -0.39 -0.51 1.00
C7 asp. Conv.,% 0.43 0.35 0.23 -0.27 0.21 -0.19 -0.02 0.39 1.00
Tab. 4 Comparison of SARA analysis data, and asphaltene conversion during processing 100% Urals VR and its blends with Middle East crudes and imported AR
Feed
100%
Urals
100%
Urals
64%
Urals /
15% BL /
21% AR
70%
Urals /
30% BL
70%
Urals /
30% BL
70%
Urals /
30%BL
85%
Urals /
15% BL
Resins,
wt.%
C7-asph,
wt.%
C5-
asph.,
wt.%
C7-asph.
D15, g/
cm3
C5-asph.
D15, g/
cm3
Feed CII
(C5-asp)
Feed CII
(C7-asp)
without slurry without slurry without slurry without slurry with 7% FCC slurry with 7% FCC slurry with 7% FCC slurry
Net conversion
(540°C+), % 55.3 64.7 67.3 72.5 75.3 74.5 71.6
ATB HFT,% 0.32 2.29 0.44 0.30 0.10 0.25 0.40
SARA composi-
tion Feed VTB Feed VTB Feed VTB Feed VTB Feed VTB Feed VTB Feed VTB
Saturates,% 25.6 34.5 22.4 26.1 17.5 25.6 22.8 23.5 20.5 22.6 22.6 19.4
Aromatics,% 53.9 44.2 66.5 51.6 67.6 56.4 53.9 51.3 57.7 51.4 57.3 53.5
Resins,% 7.8 5.6 4.9 10.3 6.8 5.8 10.8 6.7 12.1 7.5 9.2 5.7
C7 asphalte-
nes,% 12.7 15.7 6.3 12.0 8.1 12.2 12.5 17.2 9.7 18.5 10.9 21.3
C5 asphalte-
nes,% 22.2 24.5 20.5 25.8 18.4 28.5 15.9 26.0
C7 asphaltenes
D15, g/cm31.132 1.157 1.172 1.266 1.171 1.216 1.240 1.289 1.265
C5 asphaltenes
D15, g/cm31.147 1.138 1.224 1.242 1.226
C7 asphaltene
conversion,% 49.7 40.0 55.3 69.9 65.5 52.2
C5 asphaltene
conversion,% 55.2 72.4 72.0 59.9
Sulphur,% 2.9 1.1 2.9 0.9 3.3 1.3 3.7 1.6 3.3 1.4
% of design ca-
pacity, % 91.4 99.8 93.5 78.0 78.3 81.2 83.5
2nd order con-
version,% 55 64.4 64.4 74.5 76 77.2 75
REFINERY TECHNOLOGY
www.oilgaspublisher.de 11745. Edition · Issue 4/ 2019
that the vacuum residue (VR) conversion
in the investigated range of feed proper-
ties increases by decreasing feed CII (C5-
asph) and by increasing C5-asphaltene
conversion. Equation 4 suggests that an
improvement of the H-Oil feed CII can in-
crease conversion. This can be seen in the
data of Table 4. In the case 70% Urals/30%
BL without FCC slurry addition and in the
case 70% Urals/30% BL with 7% FCC
slurry addition to the feed, the feed CII
(C5asp) falls from 0.55 to 0.43 at the same
C5-asphaltene conversion of 72%. As a re-
sult the VR conversion increases from
72.5 to 75.3% and the sediment content
decreases from 0.3 to 0.1% after addition
of the FCC slurry to the H-Oil feed. In fact
the increase of conversion after addition
of 7% FCC slurry to the feed comes from
the higher reaction severity illustrated by
the higher 2nd order conversion value
(76% versus 74.5% for the case without
FCC slurry addition). Therefore the incre-
ase of H-Oil VTB (ATB) colloidal stability
by means of feed CII improvement (re-
duction) and/or asphaltene conversion
improvement (enhancement) allows an
increase in the hydrocracking reaction se-
verity, that results in a higher VR conver-
sion and higher yields of higher value
products at the expense of the lower yield
of the lower value VTB product.
As evident from Figure 3, made on the ba-
sis of the yield structure of the cases
shown in Table 4, the VTB yield continu-
ally falls with the increase of VR conversi-
on; the VGO yield peaks at about 65%
conversion; while diesel and naphtha
yields continually increase with enhance-
ment of conversion. The selectivity curves
shown in Figure 3 indicate that VGO is a
primary unstable product, while diesel
and naphtha are primary and secondary
stable products [19]. The data in Figure 3
is in agreement with the results reported
in [11] showing that diesel and naphtha
are primay and secondary stable products,
which do not undergo any conversion,
while the VGO is a primary unstable,
which converts to diesel and naphtha.
4. Conclusions
Whilst processing 24 vacuum residual
oils, obtained from crude oil blends of 15
crude oils and three imported atmosphe-
ric residual oils, in the LNB EBVR H-Oil
hydrocracker, it was found that the vacu-
um residue conversion at approximately
the same sediment level of ≈0.4% can be
predicted from the feed colloidal instabili-
ty index and the C5 asphaltene conversi-
on. The asphaltene conversion seems to
not follow the trend of increasing vacuum
residue conversion with the increase of
hydrocracking reaction severity, irrespec-
tive of the proven fact of the same reac-
tion order kinetics for both conversion
reactions. The reason for this deviation is
possibly due to the presence of asphaltene
recombination reactions taking place du-
ring the VR conversion. The Urals asphal-
tenes seem to participate easier in recom-
bination reactions in comparison with the
asphaltenes coming from crudes from the
Middle East, which leads to their lower
conversion and higher sedimentation rate
during processing 100% Urals VR. The lo-
wer the relative fraction of Urals VR in the
LNB EBVR H-Oil hydrocracker feed blend,
consisting of Urals VR and VRs from
Middle East crudes, the higher the asphal-
tene conversion and the lower the sedi-
ment content in the H-Oil ATB product
are. The asphaltene conversion can be in-
creased by a reduction of LHSV (through-
put). The aromaticity of the asphaltenes,
measured by their density, which increa-
ses with enhancement of VR conversion,
and the SARA analysis data of the H-Oil
VTB product, do not provide sufficient in-
formation to explain the different sedi-
ment levels in the different studied VTB
samples. The increase of H-Oil VTB (ATB)
colloidal stability by means of feed CII im-
provement (reduction) or/and asphaltene
conversion improvement (enhancement)
allows an increase in hydrocracking reac-
tion severity, that results in a higher VR
conversion and higher yields of higher va-
lue products at the expense of the lower
yield of the lower value VTB product.
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Dicho Stratiev is the chief process
engineer in the LUKOIL Neftohim
Burgas, Bulgaria. He is responsible
for all refinery units operation
guidance, troubleshooting support
and units performance optimization.
Professor Stratiev is an author of
more than 205 technical papers.
Ivelina Shishkova is R&D Depart-
ment Manager in the Lukoil
Neftochim Bourgas, Bulgaria. She is
REFINERY TECHNOLOGY
www.oilgaspublisher.de118 45. Edition · Issue 4/ 2019
an author of more than 60 technical papers.
Ekaterina Nikolaychuk holds BSc
degree from Ufa State Petroleum
Technological University and MSc
degree from Newcastle University.
She is a chemical engineer engineer
in the chief process engineer de-
partment of LUKOIL Neftohim Burgas, Bulgaria. She
is an author of more than 10 technical papers.
Wessel Ijlstra is technical manager
Resid, EMEAR at Shell Catalysts and
Technologies. He holds MSc in Che-
mical Engineering at University of
Twente, and MSc in Physics at Uni-
versity of Groningen.
Blaine Holmes is principal specia-
list hydroprocessing (Ebullated Bed
Technology) at Shell Projects and
Technology. He holds BSc in Chemical Engineering
at University of Calgary.
Maxime Caillot works as a Techno-
logist at Axens. He holds PhD, Cata-
lysis at Eidgenössische Technische
Hochschule Zürich, and Diplôme
d'ingénieur, Physics & Chemistry at
ENSCPB. Dr. Caillot did research in
Green Chemistry, Catalysis and Materials Chemistry.
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